Synthesis and redox properties of a chiral heterohelicene constituted of pyrrole and 1,1′‐biazulene skeletons

Chiral helicene radicals having a combination of molecular chirality and unpaired electron spin(s) are of increasing interest from both fundamental science and technological fields. We have synthesized a helicene compound, wherein a 1,1′‐biazulene skeleton is fused with an isobenzopyrrole unit that has bulky mesityl groups for steric protection. The final cyclization reaction for the target compound was accomplished very efficiently by using a microflow method. The helical structure was confirmed by X‐ray crystallography, and the optical resolution was achieved by HPLC with a chiral stationary phase. Upon one‐electron oxidation of this compound, its cation radical was successfully produced with enough stability for isolation.